Fidalgo ophiolite field trip, Part II- Mount Erie

Gabbro at Stop 1. Note the pale vertical dikes near the yellow hammer. Click any image to enlarge.

Gabbro at Stop 1. Note the pale vertical dikes near the yellow hammer. Click any image to enlarge.

A self-guided geology field trip to the second part of the Fidalgo ophiolite (oceanic crust section) is posted here. This field trip visits intrusive and sedimentary rocks on Fidalgo Island, including Mount Erie. This is the second installment in the ophiolite series, which started at the chunk of the mantle at Washington Park.

The April 12th guided geology field trip sponsored by Mount Baker Volcano Research Center will visit some of these rocks. Registration information is on the MBVRC website. If you have been waffling, time to be decisive- the trip is nearly full!

The view south from Stop 2 at Mount Erie.

The view south from Stop 2 at Mount Erie. Here we see an island in Lake Campbell, on Fidalgo Island. Skagit Bay stretches off to the south.

Geologic tour along the Dallas Road Waterfront Trail, Victoria B.C.

Dark dike of magma invaded a larger body of pale felsic magma. The dike was broken apart. This is at Holland Point. Photo by Glenn Jareshko.

Fascinating geologic relationships can be seen  at Holland Point.

The third geology field trip along the city of Victoria’s shore has been added to the website. This one walks the city’s south shore along the Dallas Road waterfront trail from Clover to Holland Points. The trip description is largely the work of Gerri McEwen, who just completed her undergraduate honors thesis on these rocks at University of Victoria.

The thrust fault has placed older rocks on top of younger rocks.

Southern Vancouver Island thrusting has placed older rocks in the hanging wall over younger rocks in the footwall. These terms are explained in the Dallas Road field trip.

The relationships between these coast rocks are complex. There has been repeated intrusion, faulting,and metamorphism during accretion of an island arc and offshore terranes against Wrangelia after the latter giant terrane had collided with North America. Do you know the meaning of the terms ‘hanging wall’ and ‘foot wall’? Go to the Dallas Road field trip webpage to better understand the origin of these terms.

Some of the rocks are beautiful and well worth the visit. Take your camera!

A bit of the mantle: Washington Park, Fidalgo Island, Washington

The 'snake-skin' texture of serpentinite lends its name to 'ophiolite'. This is a nice example near the foot of the stairs.

The ‘snake-skin’ texture of serpentinite lends its name to ‘ophiolite’. This is a nice example near the foot of the stairs.

A geology guide to ultramafic rock at Washington Park, near Anacortes, is now available on Northwest Geology Field Trips. Click here to go straight to the field trip! The rock is the metamorphic rock serpentinite, and was originally in the earth’s mantle below oceanic crust. Exposures are found along the dramatic rocky shore and on bare rocky knobs above the coastal cliffs. A single essential outcrop is highlighted in this quick self-guided field trip. The description explains what ‘ophiolite’ is and points out spectacular glacial polish at the same outcrop.

Coming soon:

  • Mount Erie- Fidalgo ophiolite Part 2
  • Finlayson Point, Victoria
  • Rock Trail, Larrabee State Park
  • ?????

Do you have field trips to share? Please do. Let’s branch out to places in southern and eastern Washington. I’m happy to help you write your guide . Contact me via comment or email:

send email here

send email here

‘Mounds’ between Sedro Woolley and Burlington

Hello Dave,
I’ve always wondered about the large “mounds”/irregularities to the East of I-5 between the Skagit and Samish rivers… They’re pretty hard to miss. How did they form, and what exactly are they?

Carston, May 29, 2013

Burlington Hill looking south from Cook Road. Click to enlarge any image.

Burlington Hill looking south from Cook Road. Click to enlarge any image.

In response to Carston,  my geologist friend Doug McKeever and I finally got around to making the jaunt south to look at these conspicuous wooded hills that rise out of the Skagit River flood plain. The greenschist and phyllite is quite interesting and very easy to get to. The driving trip is a worthwhile short detour of just a few miles when you are passing by on I-5. On a nice day the view from one of the hills over the flats is wonderful. The field trip is posted here.

Silvery phyllite and greenschist.

Silvery phyllite and greenschist on Burltingon Hill.

Giant Cairn in the Wharf Roundabout, Bellingham Washington

Some guy in a funny hat looks at the giant rock cairn in the roundabout. Hey! Wait I think I know that guy! Where're the cats?

Some guy in a funny hat looks at the giant rock cairn in the roundabout. Hey! Wait I think I know that guy! Where are the cats?

A number of Bellingham people have written me for a geological description of the 12′ rock cairn in the middle of the new roundabout at Wharf, State, Forest, and Boulevard. An article appeared in Dean Kahn’s Dec. 22 column in the Bellingham Herald; prior to that, I sent a photo and a brief notice to David B. Williams’ GeologyWriter.com blog. The 13-foot-tall stack of 4 boulders sits in the new roundabout at the south edge of downtown Bellingham. Shrubs have been planted around the cairn, but they are still spindly and short so it is still approachable on foot.

“NAME THE STACK” CONTEST! Scroll down.

The lowest two, and the uppermost, boulders are dunite from the Olivine Corporation’s Sven Larsen Quarry on the north flank of the Twin Sisters Range west of Mount Baker. (48° 44.640′ N , 122° 0.345′ W.) The stone second from the top is serpentinite. It also came from the quarry. The stones were supplied by Princess Jade, a stone-supply company in Everson Washington. Get up close enough to see the smooth highlights on the serpentinite boulder, polished by Princess Jade prior to installation. The 8-mile-long Twin Sisters Range is a narrow slab of mantle dunite, among the largest in the world, faulted upward into the crust during plate collisions, and exposed by erosion.

The dunite boulders feature tiny black chromite crystals surrounded by olivine.

The dunite boulders feature tiny black chromite crystals surrounded by olivine.

Dunite is a dense crystalline rock. By definition, it consists of around 90% olivine crystals; the remainderis pyroxene and chromite. Dunite is believed to be the residue left behind when basaltic magma forms in the mantle, typically deep in subduction zones. Water carried into the mantle via the subducted ocean plate (the ‘slab’) lowers the melting point of the mantle, generating basaltic melt. The lower density basalt magma rises upward through the mantle taking lighter minerals such as silica along for the ride, leaving behind the denser minerals – olivine and pyroxene. Serpentinite is a low-temperature metamorphic rock formed when water enters the molecular structure of ultramafic rocks such as dunite. Hydrated olivine becomes a different mineral, serpentine.

Polished highlights on the softer serpentinite boulder.

Polished highlights on the softer serpentinite boulder.

The City of Bellingham had a choice of two designs incorporating the large boulders. The stack won out over the other possibility, scattering the rocks on the ground. Bellingham’s mayor, Kelli Linville, said “The landscaping we chose reflects the natural beauty of our area. Since cairns are traditionally used to help people find their way, a cairn is an appropriate part of the landscape at this important crossroads in our community.” (Bellingham Herald, Dec 22, 2013). According to Sam Shipp, the project engineer at Bellingham’s Public Works Department, the cairn option helps protect drivers from the glare from oncoming headlights and directs drivers’ vision toward other vehicles approaching from the left inside the roundabout, as well as providing an aesthetic component.

Dunite is very dense, about 3.3 grams/cubic cm. Serpentinite is around 2.7 g/cc. Contrast that with basalt (2.8-3 g/cc), andesite (2.5-2.8) and granite 2.6-2.7). The largest stone, the one on the bottom, weighs around 15.5 tons. The two in the middle are 8.5 tons each, and the little one on top is about 3.5 tons. The four stones are held upright by a central steel rod sunk into a concrete base. The project cost $75,000.

OK. “NAME THE STACK” CONTEST! Let’s name that stack o’ rocks! Submit your suggestions via comment and I’ll forward them to the City via my very special confidential connection.

Guided geology field trip by Dave Tucker: Baker River trail June 8th

Dear friends,

An alluvial fan is perfectly exposed in cross section along the Baker River trail.

An alluvial fan is perfectly exposed in cross-section along the Baker River trail.

Mount Baker Volcano Research Center is offering a field trip up the Baker River on June 8th. It is a fundraiser for the non-profit, and I’ll be leading it, along with Doug McKeever (Whatcom Community College) and Sue Madsen (Skagit Fisheries Enhancement).

Highlights include:

  • Shuksan greenschist (metamorphosed subducted seafloor basalt) which is the local bedrock;
  • new salmon restoration facilities;
  • an active alluvial fan;
  • river erosion and deposition;
  • a great variety of rocks in river bars;
  • rock slides;
  • a fantastic ‘faerie forest’ of lichen-draped maples.
  • If the weather be good- fabulous views into the heart of the North Cascades.

Cost is $75, includes van transport and a trip guide.

For info and registration, go to:

http://mbvrc.wordpress.com/2013/05/08/mbvrc-geology-field-trip-june-8th-geo-potpourri-plus-salmon-ecology/

An unnamed waterfall plummets hundreds of feet over a wall of metamorphic bedrock along the trail. Click to enlarge any photo.

An unnamed waterfall plummets hundreds of feet over a wall of metamorphic bedrock along the trail. Click to enlarge any photo.

Pillows in the Middle Fork Nooksack

Stacked pillows. Stolen from a commercial website. So, sue me.

Stacked pillows. Stolen from a commercial website. So, sue me.

(Click HERE to go straight to the page about the pillows along the road.)

No, pillow lava, silly!

Cross-sectioned basalt lava pillow in the Elbow Lake Formation, Middle Fork Nooksack Road. Click to enlarge.

Cross-sectioned basalt lava pillow in the Elbow Lake Formation, Middle Fork Nooksack Road. Click to enlarge.

I planned a XC ski trip up the Porter Creek Road or elsewhere off the Middle Fork Road today, but it was raining and 41 degrees. Indulging my secret identity as a geologist, I instead poked around in a roadside quarry, looking at pillow lava in the Elbow Lake Formation. A rewarding outing from Bellingham if you have a 2-3 hours on your hands and a deeply felt need to look at some exotic, unusual, and (admittedly) not too beautiful rocks. The saving grace is the lava pillows, and a cup of coffee on the way and on the way back. As an added bonus, there is access to Twin Sisters dunite nearby.

P.S. There ARE some nice roads to ski up and back down off the Middle Fork.

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